114 lines
3.3 KiB
Rust
114 lines
3.3 KiB
Rust
// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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//! The Finally trait provides a method, `finally` on
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//! stack closures that emulates Java-style try/finally blocks.
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//!
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//! Using the `finally` method is sometimes convenient, but the type rules
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//! prohibit any shared, mutable state between the "try" case and the
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//! "finally" case. For advanced cases, the `try_finally` function can
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//! also be used. See that function for more details.
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//!
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//! # Example
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//!
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//! ```
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//! use std::finally::Finally;
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//!
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//! (|| {
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//! // ...
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//! }).finally(|| {
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//! // this code is always run
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//! })
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//! ```
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#![experimental]
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use ops::Drop;
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/// A trait for executing a destructor unconditionally after a block of code,
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/// regardless of whether the blocked fails.
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pub trait Finally<T> {
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/// Executes this object, unconditionally running `dtor` after this block of
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/// code has run.
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fn finally(&mut self, dtor: ||) -> T;
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}
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impl<'a,T> Finally<T> for ||: 'a -> T {
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fn finally(&mut self, dtor: ||) -> T {
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try_finally(&mut (), self,
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|_, f| (*f)(),
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|_| dtor())
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}
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}
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impl<T> Finally<T> for fn() -> T {
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fn finally(&mut self, dtor: ||) -> T {
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try_finally(&mut (), (),
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|_, _| (*self)(),
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|_| dtor())
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}
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}
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/// The most general form of the `finally` functions. The function
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/// `try_fn` will be invoked first; whether or not it panics, the
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/// function `finally_fn` will be invoked next. The two parameters
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/// `mutate` and `drop` are used to thread state through the two
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/// closures. `mutate` is used for any shared, mutable state that both
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/// closures require access to; `drop` is used for any state that the
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/// `try_fn` requires ownership of.
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///
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/// **WARNING:** While shared, mutable state between the try and finally
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/// function is often necessary, one must be very careful; the `try`
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/// function could have panicked at any point, so the values of the shared
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/// state may be inconsistent.
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///
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/// # Example
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///
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/// ```
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/// use std::finally::try_finally;
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///
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/// struct State<'a> { buffer: &'a mut [u8], len: uint }
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/// # let mut buf = [];
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/// let mut state = State { buffer: &mut buf, len: 0 };
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/// try_finally(
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/// &mut state, (),
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/// |state, ()| {
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/// // use state.buffer, state.len
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/// },
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/// |state| {
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/// // use state.buffer, state.len to cleanup
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/// })
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/// ```
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pub fn try_finally<T,U,R>(mutate: &mut T,
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drop: U,
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try_fn: |&mut T, U| -> R,
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finally_fn: |&mut T|)
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-> R {
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let f = Finallyalizer {
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mutate: mutate,
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dtor: finally_fn,
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};
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try_fn(&mut *f.mutate, drop)
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}
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struct Finallyalizer<'a,A:'a> {
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mutate: &'a mut A,
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dtor: |&mut A|: 'a
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}
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#[unsafe_destructor]
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impl<'a,A> Drop for Finallyalizer<'a,A> {
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#[inline]
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fn drop(&mut self) {
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(self.dtor)(self.mutate);
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}
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}
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